Field of the Invention
The invention relates to cellulosic man-made fibers with permanently flame-retardant properties whereby the flame-retardant property is arrived at by adding an oxidized condensate of tetrakis hydroxyalkyl phosphonium salt with ammonia and/or a compound containing nitrogen which contains one or several amine groups, to the spinning mass and/or the spinning solution and the fiber reveals a strength (tensile strength) in the conditioned state of more than 18 cN/tex.
Description of the Related Art
The cellulosic man-made fibers can be viscose/modal, cupro, or lyocell fibers. Lyocell fibers are defined by BISFA (The International Bureau for the Standardization of Man-made Fibers) as cellulosic man-made fibers which are spun from an organic solvent without the derivatisation of the cellulose (the direct spinning process). This also means fibers which are spun from solutions of cellulose in ionic liquids.
An overview of the methods used to render cellulosic textiles flame-retardant and the mechanisms used for this is supplied by the publication: Horrocks, A. R.; Kandola, B. K. “Flame Retardant Cellulosic Textiles” Spec. Publ.—Royal Society of Chemistry, volume 224, year 1998, pages 343-362. The methods described differ in the element responsible for the flame-retardation (mainly phosphorus, however, nitrogen, boron and sulphur as well), the place of the application (surface treatment mainly with cotton, additive in fiber production with man-made fibers) and the permanency (degree of resistance of flame-retardant properties to laundering treatments).
A large share of the permanently flame-retardant cellulosic textiles is produced by finishing cotton fabrics with tetrakis (hydroxymethyl)phosphonium derivatives (e.g. Proban® finish) respectively with N-methylol dialkylphosphonopropionamides (e.g. Pyrovatex CP®). The finished textiles do, however, have a very hard hand.
Among the cellulosic man-made fibers, a large number of substances were suggested as flame-retardant additives for viscose fibers in fiber production.
In U.S. Pat. No. 3,266,918 Tris(2,3-bromopropyl)phosphate is suggested as the flame-retardant agent. A fiber of this kind was produced for some time on an industrial scale. Production was, however, discontinued due to the toxicity of the flame-retardant agent.
A class of substances used as a flame-retardant agent is that of substituted phosphazenes. A flame-retardant viscose fiber was produced at industrial level on the basis of these substances (U.S. Pat. No. 3,455,713). The flame-retardant agent is however in liquid form and can only be spun into viscose fibers with a lower yield (approx. 75 weight percent) and it tends to migrate out of the fiber thus giving the fiber an undesirable stickiness.
Similar compounds were described in patents but were never tried for viscose fibers on an industrial scale (BP 1,521,404; U.S. Pat. Nos. 2,909,446, 3,986,882; JP 50046920; DE 2,429,254; GB 1,464,545; U.S. Pat. No. 3,985,834; 4,083,833; 4,040,843; 4,111,701; 3,990,900; 3,994,996; 3,845,167; 3,532,526; 3,505,087; 3,957,927). All of these substances are in liquid form and demonstrate the same disadvantages as in U.S. Pat. No. 3,455,713.
Apart from the above named Tris(2,3-bromopropyl)phosphate, a series of other organophosphates respectively phosphonic acid amides and esters were described as flame-retardant agents for viscose fibers (DE 2,451,802; DE 2,622,569; U.S. Pat. Nos. 4,193,805; 4,242,138; JP 51-136914; DE 4,128,638).
Of this class of substances, until now only the compound 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2 fulfils the requirements with regard to the effectiveness (the necessary amount of incorporation in order to fulfil EN ISO 15025:2002), quantitative yield in the spinning process and halogen free.
Apart from the phosphorus compounds mentioned above, flame-retardant viscose fibers were described which contain silicic acid (EP 619,848; EP 1,753,900; EP 1,918,431). These fibers pass the flame test described above, however, only with high contents of silicic acid. Due to the high content of pigment which does not contribute to the tenacity, the fibers do not attain the necessary fiber tenacities required for textile applications.
In a series of patent applications, ways were described to impart flame-retardant properties to cellulosic fibers, which are produced according to the amine oxide-process. WO 93/12173 describes triazine compounds containing phosphorus as a flame-retardant agent for plastic materials, in particular polyurethane foam. Cellulose is mentioned in claim 18, spun from a solution in a tertiary amine oxide, without citing an example with regard to the actual suitability of the compounds as flame-retardant agents for cellulose.
WO 94/26962 describes the addition of a tetrakis hydroxymethyl phosphonium chloride (THPC)—urea—pre-condensate to the wet fiber prior to drying, ammonia-treatment, condensation, oxidation and drying after a second washing step. However, condensation reactions at fiber level significantly impair the fiber properties (embrittlement).
In WO 96/05356, lyocell fibers are treated with phosphoric acid and urea and kept at 150° C. for 45 minutes. This process also damages the mechanical properties of the fibers to a considerable extent.
EP 0 836 634 describes the incorporation of compounds containing phosphorus as flame-retardant agents for regenerated cellulose fibers, particularly lyocell fibers. 1,4-diisobutyl-2,3,5,6-tetrahydroxy-1,4-dioxophosphorinane is cited as an example. The process has the disadvantage that the incorporation yield of the flame-retardant agent only equals 90% and thus problems occur in the closed solvent loops involved in the lyocell process.
U.S. Pat. No. 6,893,492 and WO 2007/022552 describe clay minerals (montmorillonite and/or hectorite) as an additive for lyocell fibers. The flame-retardant effect of these additives does not, however, suffice for textile products, which have to pass the vertical flame test, according to EN ISO 15025:2002 process B—edge flaming.
In the Korean patent application, Kongkae Taeho Kongbo 2009/025979, a flame-retardant agent containing phosphorus is bonded to the cellulose via a silicon-oxygen group. This bond is, however, sensitive to hydrolysis and so the product is not suitable for washables.
None of the methods described for the lyocell process has become important in technical terms. One important reason for this is that the closed solvent loops in this process place special demands on the yield when incorporating a solid or liquid additive in the spinning mass. The recovery of solvent equals more than 99%. Even small amounts of impurities which get into the spinning bath/washing water build up in the closed solvent loops as a result of the non quantitative yield of incorporation and lead to problems when spinning and when reprocessing/cleaning the solvent.
No patent applications have been announced to date for flame-retardant lyocell fibers, made from ionic liquids (“ionic liquids”). Likewise no patent applications are known for fibers according to the cupro or carbamate process. According to BISFA, cupro fibers are a separate fiber genre. In the following, fibers according to the carbamate process are called carbamate fibers.
The use of tetrakis hydroxymethyl phosphonium chloride (THPC)—urea—pre-condensates for the flame-retardant finishing of in particular cotton, involving the process steps impregnation with the precondensate—treatment with ammonia—condensation—oxidation (e.g. the Proban®—process), is known.
The use of fully condensed products is described in U.S. Pat. No. 3,645,936. According to the teaching of the patent, the incorporation of an ammonia/tetrakis hydroxymethyl phosphonium chloride—polymer (THPC/NH3-polymer) solely with the amount of incorporation which is required to pass the flame test (20%), leads to fibers of insufficient tenacity (1.08 g/den=approx. 9.7 cN/tex).